L. vannamei is the species which has been farmed most productively among all penaeidae shrimp in China or even in the world. At present, the world average annual output is more than 3,000 thousand tonnes. Like other prawn species, L. vannamei has significant difference between female and male individuals in size. The growth rate of female individuals at the middle and later stage is far higher than that of male individuals. Thus, the mono-sex control of L. vannamei is useful in order to culture a mono-sex population, thereby having important significance to increase the output and benefit of the prawn culture industry.
Identification of the genetic sex of an individual is the basis for realizing the culture of a mono-sex population of L. vannamei. Though the sexes of female and male shrimp can be identified through the morphological external sex characters when shrimps grown to a certain stage. In scientific research and actual production, if early identification of sexes can be realized by a molecular method at the juvenile stage, experiments and culture can be undertaken specifically to individuals of a certain sex, so that the efficiency of the scientific research and actual production can be greatly improved.
In the research of sex markers for prawns, there were already some reports of sex marker screening, for example, Staelens et al. (Staelens, J Rombaut, D., Vercauteren, I., Argue, B., Benzie, J. and Vuylsteke, M. High-density linkage maps and sex-linked markers for the black tiger shrimp (Penaeus monodon). Genetics, 2008, 179(2): 917-925.) constructed a high-density genetic linkage map for P. monodon, and found two sex difference markers in the genetic linkage map. It was validated that the markers could be used as markers for sex identification in a population of P. monodon from other genetic sources. Moreover, the team also applied for a relevant patent (Chinese invention patent No. 200780015173.9, entitled “Sex-Specific Markers for Shrimps and Prawns”). However, the markers could not be used for the sex identification of L. vannamei due to the difference between prawn species. In the study of L. vannamei, Zhang et al. (Zhang, L., Yang C., Zhang, Y, Li, L., Zhang, X., Zhang, Q., Xiang, J. A genetic linkage map of Pacific white shrimp (Litopenaeus vannamei): sex-linked microsatellite markers and high recombination rates. Genetica, 2006, 131(1): 37-49) screened a sex-specific microsatellite site of L. vannamei by means of a QTL mapping method. However, it was validated that the microsatellite marker was family specific and could not be used as a marker for sex identification in other sourced population. Similarly, Alcivar-Warren et al. (Alcivar-Warren, A., Meehan-Meola, D., Park, S. W., Xu, Z., Delaney, M., Zuniga, G. Shrimp Map: A low-density, microsatellite-based linkage map of the pacific white leg shrimp, L. vannamei: Identification of sex-linked markers in linkage group 4. Journal of Shellfish Research, 2007, 26(4): 1259-1277) also found sex-specific microsatellite markers of L. vannamei, but the markers were only restricted to the researched population. In the research of Fenneropenaeus chinensis, though more linkage maps were constructed, no corresponding sex identification markers were reported (Li, Z. X., Li, J., Wang, Q., He, Y., Liu, P. AFLP-based genetic linkage map of marine shrimp Penaeus (Fenneropenaeus) chinensis. Aquaculture, 2006, 261(2): 463-472; Sun, Z. N., Liu, P., Li, J., Meng, X., Zhang, X. Construction of a genetic linkage map in F. chinensis (Osbeck) using RAPD and SSR markers. Hydrobiologia, 2008, 596: 133-141; Liu, B., Wang, Q., Li, J., Liu, P., He, Y A genetic linkage map of marine shrimp Penaeus (Fenneropenaeus) chinensis based on AFLP, SSR, and RAPD markers. Chinese Journal of Oceanology and Limnology, 2010, 28(4): 815-825.). By means of gene differential expression analysis, one gene showed differential expression between female and male of F. chinensis was screened out (Li, S., Li, F., Xie, Y, Wang, B., Wen, R., Zhang, C., Yu, K., Xiang, J. Screening of Genes Specifically Expressed in Males of F. chinensis and Their Potential as Sex Markers. Journal of Marine Biology, 2013, 1-9.), and the marker was developed as a marker for female and male sex identification (Chinese invention patent, No. 101709332A). However, so far, no markers for sex identification of L. vannamei have been reported.